Permeability Contrast Controls Inter-Layer Interference and Sweep Efficiency During Supercritical CO2 Miscible Flooding

Multi-layer combined development is widely adopted in low-to-medium-permeability sandstone reservoirs to balance economic efficiency and development performance during supercritical CO2 miscible flooding. However, permeability heterogeneity often induces severe inter-layer interference and gas channeling. To quantitatively clarify the dynamic influence of permeability heterogeneity on commingled injection and production systems, this study conducted single-core baseline tests (ranging from 19.17 mD to 205.60 mD) and three-core parallel physical simulation experiments at 150 °C and 50 MPa with varying permeability contrasts (nominal ratios of 5, 7, and 10; actual ratios of 5.15, 7.22, and 10.73, by fixing the medium- and low-permeability layers). The experimental results demonstrate that recovery increased with permeability across the tested assemblies, with single-core ultimate recovery increasing monotonically from 64.69% to 78.68% as permeability rises, accompanied by earlier CO2 breakthrough and lower peak pressure drops. In parallel combined development systems, permeability contrast serves as the dominant factor associated with inter-layer flow competition and dynamic shielding. At a high permeability contrast of 10, the high-permeability layer in the combination experiences premature gas breakthrough, with instantaneous split ratios generally between 60% and 85% (mean 71.63%) and consistent with substantial pressure relief. The observed zero recovery in the low-permeability layer is consistent with a dynamic shielding mechanism, in which early pressure relief in the high-permeability layer is interpreted as limiting the driving pressure drop available for low-permeability mobilization. As the permeability contrast decreases to 7 and 5, the flow resistance imbalance is significantly mitigated, allowing the low-permeability layer’s recovery factor to increase to 19.06% and 38.49%, respectively. At nominal ΔK = 5, this corresponds to a 26.20 percentage-point deficit and a 40.50% relative suppression compared with its single-core baseline (64.69%). Furthermore, system overall recovery improves substantially from 45.27% to 59.91%, and cumulative gas–oil ratios drop noticeably. The smallest tested permeability contrast gave the highest combined recovery under the experimental conditions. This is an experimentally observed case, not a general or calibrated threshold. The novelty of this work lies in providing a controlled-variable three-core parallel dataset under supercritical miscible conditions, providing macroscopic evidence interpreted as dynamic shielding of low-permeability layers, and identifying the smallest tested permeability contrast as a reference condition for optimized sweep efficiency. This study provides crucial physical simulation support and technical references for rational layer-combination division, stratified gas injection strategies, and subsequent mobility control optimization in heterogeneous reservoirs.